Preparation And Properties Of Thermally Conductive And Electrically Insulating Graphene/Silicone Composites

With the rapid development of semiconductor technology in recent years,the electronic field has suffered from the overheating problem of devices,which also raised higher requirements for thermally conductive but electric insulation materials.Silicone rubber is widely used as thermal interface materials(TIMs)and electronic package materials because of its good mechanical properties,superior electrical insulation performance,excellent temperature resistance and good chemical inertness.However,because of the low thermal conductivity of silicon rubber,it is necessary to add inorganic metal oxides with high thermal conductivity such as Al2O3,AlN,BN etc.to improve the thermal conductivity of the matrix.However,high filler loading is essential for traditional inorganic fillers in order to enhance the thermal conductivity of the polymer matrix effectively.The higher filler content not only reduces the mechanical properties of the composites,but also increases the viscosity of the composites.Besides,high viscosity makes it difficult to blend fillers and matrix uniformly.to develop high performance thermal interface materials has become an urgent demand in this field.It is of urgent demand for developing high performance thermal interface materials in this field.Graphene possesses extremely high thermal conductivity and has been regarded as a prominent candidate to be used in thermal management of electronic components.Since its discovery in 2004,graphene has attracted wide attention in the field of thermal conductive composites because of its excellent intrinsic thermal conductivity(?5000W/m·K).However,the addition of graphene inevitably causes dramatic decrease in electrical insulation performance,which restrict its application as high performance thermal interface materials greatly.Hence,it is of great significance to fabricate graphene/silicone composites with both high thermal conductivity and satisfactory electrical insulation in electronic thermal management field.In this study,in order to fabricate thermally conductive but insulating graphene/silicone rubber composites,nano silicon dioxide particles modified graphene filler(SiO2@GNP)and high density polyethylene(HDPE)modified graphene filler(HDPE@GNP)were prepared by sol-gel method and solution crystallization method respectively.Silicone rubber based composites was prepared after blending the two kinds of fillers with polydimethylsiloxane(PDMS)through solution casting process.The effects of different kinds of filler and filler content on the volume resistivity,thermal conductivity and hardness of the composites werestudied.Due to the similarity in the chemical structure between inorganic silicon dioxide and silicone rubber,the nano SiO2 insulation coating layer on the surface of graphene improved the dispersion of graphene in silicone rubber matrix and reduce the aggregation of the fillers.When the mass fraction of GNP in SiO2@GNP/PDMS composites is 2%,the thermal conductivity of the composites reaches 0.51 W/m · K,which is 162%higher than that of pure PDMS matrix.However,the volume resistivity of the composite remained in the insulator area of 1012·cm.Meanwhile,the addition of SiO2@GNP did not significantly improve the hardness of the composite.The HDPE crystal has higher thermal conductivity than the PDMS matrix due to the contribution of heat transfer through lattice vibration.After surface modification of graphene with HDPE crystal,although the heat conduction mechanism through electron is blocked,the heat flux can be transmitted through phonons in HDPE.When the mass fraction of GNP in the HDPE@GINP/PDMS composite is 2%,the thermal conductivity of the composites reaches 0.47 W/m · K,which is 143%higher than that of the PDMS matrix.Due to the excellent electrical insulation performance of HDPE,the volume resistivity of composite material is only one order of magnitude lower than that of pure PDMS matrix.The excellent properties of composites are mainly attributed to the effective insulating coating layer on the surface of graphene,the intrinsic high thermal conductivity of' graphene,and uniform dispersion of fillers in matrix.This thermally conductive but electrically insulating graphene/silicone composite material is expected to be applied as high performance thermal interface materials in the future.